Superconductive junctions with trappinglayers for the detection of X-rays

Abstract

Addition of a trapping layer to an SIS junction improves its performance as an Xray detector. In this article X-ray induced pulse height and decay time spectra will be presented as a function of bias voltage. These measurements are in good agreement with a description based on the time constants for trapping, excitation and tunneling calculated by means of a model for proximity layers developed by Golubov et al.. 1'2The interpretation of the data doesn't require an initial fast loss process for the created quasi-particles as discussed by Van Vechten. 3

Field dependence on the Josephson current and Fiske resonances in specially shaped Josephson junctions

“…The resonance voltages of the "quartic with cross" junction (3) are shown in Table 1, and are quite similar to those measured for the quartic junction (1). The influence of the internal structures on the resonance voltages seems to be quite small.…”

“…5(a), although some differences can be observed. The first two resonances (F1 and F2) for junctions (1) and (3), have almost the same field dependence, except for the small second lobe in F2 for junction (3). A fairly strong resonance (F3) was observed at the same voltage as for junction (1), but we were not able to measure the field dependence.…”

“…When a junction is used to detect X-ray photons or other high-energetic particles, it is most often current biased in the subgap regime [1]. The unwanted switching to either the Josephson zero-voltage state, or to a Fiske resonance, hampers the stable operation as a particle detector.…”

Superconducting particle detectors

“…In addition the minimal tunnelling noise may be achievable as it is possible to have P 2 ∼ 0 in equation ( 16). This feature has been implemented by le Grand et al using a Ta sink on Nb [94,95] and Porter et al using a Au/Pd contact on a portion of the Nb counterelectrode [96]. The spectrum of charge pulses for this latter geometry, reproduced in figure 17, shows a single-peak structure and an energy resolution of 68 eV at 5.89 keV.…”

“…Sometimes it is necessary to purposely trap flux in order to suppress the Fiske steps which result from the ac Josephson effect [99,100], and which can lead to instability of the bias point, particularly for seriesconnected arrays of STJs [101]. For some materials, such as Nb, qp loss into normal metal surface oxides [102] is a significant problem [95].…”